Polymeric fiber webs with binder comprising salt of inorganic acid

ABSTRACT

Provided are nonwoven polymeric fiber webs using an improved curable composition. Such curable composition comprises an aldehyde or ketone and an amine salt of an inorganic acid. The composition when applied to polymeric fibers is cured to form a water-insoluble polymer binder which exhibits good adhesion and thermodimensional stability.

BACKGROUND

The subject invention pertains to polymeric fiber webs with an improvedbinding composition and load bearing at elevated temperatures. Morespecifically, the invention pertains to non-woven polymeric fiber websusing an improved curable composition comprising an amine salt of aninorganic acid. An aldehyde or ketone is added to the salt to form acomposition which upon curing is capable of forming a water-insolublepolymer. Once applied to the polymer fibers, the binding composition iscured.

Nonwoven webs comprised of polymeric fibers have a variety ofapplications. The applications can range from prepeg laminates;polishing or abrasive pads; separators for alkali battery cells;laminated materials for electrical circuit boards; filters, both for gasand liquids; diapers; towels; wipes; industrial and medical garments;foot covers; sterilization wraps, etc.

In many of the applications, the polymeric fibers of the nonwoven webmust exhibit good physical properties such as chemical resistance andheat resistance. The nonwoven web is many times used in a hazardousenvironment, and therefore demands are placed on its construction. Thiswould include not only the polymeric fibers, but also the binder used inthe nonwoven web. Many different binders have been used in the past fornonwoven polymeric fiber webs.

For example, in U.S. Pat. No. 7,026,033, a heat resistant nonwoven webcomprised of organic synthetic fibers also uses an organic resin binder.The binder is selected from an epoxy resin, phenol resin, melamineresin, formaldehyde resin and fluropolymer resin.

U.S. Pat. No. 7,534,163 describes a non-woven fabric for a polishing padused to polish semi-conductors. The fibrous component of the pad can beselected among polyester, polypropylene, polyamide, acrylic,polyethylene and cellulosic materials. The binder used for the padincludes resins of polyurethanes, polyacrylates, polystyrenes,polyamides, polycarbonates and epoxies.

Economies without sacrificing physical properties is always a concern inpreparing such non-woven polymeric fiber webs. The industry continuouslysearches for non-woven polymeric fiber webs that can provide thephysical properties needed to achieve the required performance, butwhich offer an economic advantage.

Accordingly, in one aspect the present invention provides a novelnonwoven polymeric fiber web comprised of a non-phenol-formaldehydebinder.

Another aspect of the invention provides a novel nonwoven polymericfiber web with a binder which provides advantageous flow properties, thepossibility of lower binder usage, the possibility of overall lowerenergy consumption, increased sustainability of the raw materialsutilized in the formation of the binder, considerable reduction in theuse of petroleum based ingredients, elimination of process corrosion,elimination of interference in the process by a silicone, and improvedoverall economics.

Still another aspect of the present invention is to provide a nonwovenpolymeric fiber web which uses a suitable binder having improvedeconomics, while also enjoying improved physical properties, includingchemical resistance and heat resistance.

These and other aspects of the present invention will become apparent tothe skilled artisan upon a review of the following description and theclaims appended hereto.

SUMMARY OF THE INVENTION

Provided is a nonwoven web comprised of polymeric fibers. The binder isa curable composition comprising a mixture of an aldehyde or ketone andan amine salt of an inorganic acid. This composition upon curing iscapable of forming a water-insoluble polymer.

A process for preparing the nonwoven web of polymeric fibers is alsoprovided, comprising applying to the polymeric fibers a composition as abinder comprising an aldehyde or ketone and an amine salt of aninorganic acid. Thereafter the composition is cured while present on thepolymeric fibers to form a water-insoluble polymer.

In a preferred embodiment the resulting non-woven product is a mat. Thenon-woven product is useful in a roofing membrane. In other embodimentsthe non-woven product is a filter or separator for alkali battery cells.

BRIEF DESCRIPTION OF THE FIGURE OF THE DRAWING

Machine and cross-machine direction tensile elongation and elevatedtemperature relative tensile elongation of a HMDA/Phos/Dextrose binderare graphically expressed as a ratio to a standard latex binder system.The MD and CMD tensile elongation tests were conducted at roomtemperature. The relative tensile elongation tests were conducted at200° C. and the absolute elongation is determined at tensile loadings of5, 8, and 12 daN, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The polymeric fibers that can be used in preparing the nonwoven webs andproducts can be any useful synthetic fibers, preferably syntheticorganic fibers. The fibers, upon application of the unique binder of thepresent invention, are formed into a nonwoven web. Such nonwoven webshave numerous applications, such as prepeg laminates; polishing,abrasive or cleaning pads; separators for alkali cells; filters forliquids or gases; laminated materials for electrical circuit boards;diapers; wipes; industrial garments; foot covers; sterilization wraps,etc. Of particular application are such nonwoven webs in hazardousenvironments requiring chemical and high temperature tolerance. Thesynthetic fibers in combination with the particular binder of thepresent invention allows one to achieve a nonwoven web that can meet therequirements of all the foregoing applications.

Among the fibers which can be used to form the nonwoven webs arepolyester, polypropylene, polyamide, acrylic, polyethylene, cellulosic,sulfones, polysulfones, polyether ketones, polysiloxanes, polybutylene,halogenated polymers such as polyvinyl chloride, polyaramids, melamineand melamine derivatives, polyurethanes, copolymers thereof andcombinations thereof. Bicomponent fibers can be used, wherein the coreand sheath materials may be different from one another, or in aside-by-side configuration. The nonwoven webs can be formed by applyinga binder to the fibers using conventional techniques. However, aparticular binder is employed in preparing the nonwoven webs of thepresent invention.

The binder of the present invention which is employed to prepare thenonwoven web of polymeric fibers is a curable composition comprising analdehyde or ketone and an amine salt of an inorganic acid.

The salt can be any amine salt of an inorganic acid. This includesammonium salts and amine-acid salts, which are considered amine salts.Any suitable inorganic acid can be used. The acids can be oxygenatedacids or non-oxygenated acids. Examples of suitable oxygenated acidsinclude, but are not limited to, phosphoric acid, pyrophosphoric acid,phosphorus acid, nitric acid, sulfuric acid, sulfurous acid, boric acid,hypochloric acid and chlorate acid. Examples of non-oxygenated acidsinclude, but are not limited to, hydrochloric acid, hydrogen sulfide andphosphine. Phosphoric acid is most preferred.

The salt can be prepared using any conventional technique to createsalts of inorganic acids. Ammonium salts of an inorganic acid, e.g.,phosphoric acid, is one of the preferred salts. Reacting ammonia withthe acid will yield the salt. Amine-acid salts are also preferred, withsuch salts obtained by reacting the selected amine with the acid inwater. This is a very simple and straightforward reaction. The molarratio of acid functionality to amine functionality can vary, and isgenerally from 1:25 to 25:1. More preferred is a ratio of from 1:5 to5:1, with a ratio of about 1:2 to 2:1 being most preferred.

Example of amines include, but are not limited to, aliphatic,cycloaliphatic and aromatic amines. The amines may be linear orbranched. The amine functionalities may be di- or multifunctionalprimary or secondary amines. The amines can include otherfunctionalities and linkages such as alcohols, thiols, esters, amides,acids, ethers and others.

Representative amines that are suitable for use in such an embodimentinclude 1,2-diethylamine, 1,3-propanediamine, 1,4-butanediamine,1,5-pentanediamine, 1,6-hexanediamine, α, α-diaminoxylene,diethylenetriamine, triethylenetetramine, tetraethylenepentamine, andmixtures of these. A preferred diamines for use in this embodiment ofthe invention are 1,4-butanediamine and 1,6-hexanediamine. Natural andsynthetic amino acids such as lysine, arginine, histidine, etc can alsobe used.

To the solution of amine salt of inorganic acid, the carbonyl functionalmaterials can be added, especially an aldehyde or ketone. Due to theirhigher reactivity, aldehydes are preferred to ketones. The compositioncomprises the amine salt of an inorganic acid and the aldehyde and/orketone. Some small amount of reaction does take place within thecomposition between the components. However, the reaction is completedduring the curing step, followed by the cross-linking reaction ofcuring.

Examples of suitable aldehydes include, but are not limited to, mono-and multifunctional aldehydes including acetaldehyde, hydroxyacetaldehyde, butyraldehyde, acrolein, furfural, glyoxal,glyceraldehyde, glutaraldehyde, polyfurfural, poly acrolein, copolymersof acrolein and others. Reducing mono, di- and polysaccharides such asglucose, maltose, celobiose etc. can be used, with reducingmonosaccharides such as glucose being preferred.

Examples of ketones include, but are not limited to, acetone, acetylacetone, 1,3 dihydroxy acetone, benzil, bonzoin, fructose, etc.

The carbonyl compound, i.e., the aldehyde or ketone, reacts with theamine salt of the inorganic acid. The amount of aldehyde and/or ketoneadded is generally such that the molar ratio of acid in the amino-amideor ammonium salt intermediate to carbonyl or ketone is from 1:50 to50:1. A ratio of 1:20 to 20:1 is more preferred, with a ratio of 1:10 to10:1 being most preferred.

The composition when applied to the polymeric fibers optionally caninclude adhesion prompters, oxygen scavengers, solvents, emulsifiers,pigments, fillers, anti-migration aids, coalescent aids, wetting agents,biocides, plasticizers, organosilanes, anti-foaming agents, colorants,waxes, suspending agents, anti-oxidants, crosslinking catalysts,secondary crosslinkers, and combinations of these.

The composition of the present invention can be applied to the polymericfibers by a variety of techniques. In preferred embodiments theseinclude spraying, spin-curtain coating, and dipping-roll coating. Thecomposition can be applied to freshly-formed polymeric fibers, or to thepolymeric fibers following collection. Water or other solvents can beremoved by heating.

Thereafter the composition undergoes curing wherein a strong binder isformed which exhibits good adhesion to the polymeric fibers. Such curingcan be conducted by heating. Elevated curing temperatures on the orderof 100 to 300° C. generally are acceptable, but below the meltingtemperature of the polymeric fibers. Satisfactory curing results areachieved by heating in an air oven at 200° C. for approximately 20minutes.

The cured binder at the conclusion of the curing step commonly ispresent as a secure coating in a concentration of approximately 0.5 to50 percent by weight of the polymeric fibers, and most preferably in aconcentration of approximately 1 to 25 percent by weight of thepolymeric fibers.

The present invention provides a formaldehyde-free route to form asecurely bound formaldehyde-free product. The binder composition of thepresent invention provides advantageous flow properties, the eliminationof required pH modifiers such as sulfuric acid and caustic, and improvedoverall economics and safety. The binder also has the advantages ofbeing stronger and offering lower amounts of relative volatile organiccontent during curing, which ensures a safer work place and environment.The cure time of the binder is also faster and therefore does favor theeconomics while reducing the energy consumption during the curingprocess and lowering the carbon footprint. The binder also contains highlevel of sustainable raw materials further reducing the dependency tofossil based sources for the resin. Due to the hydrophobic nature of thepresent invention, the need for a water repellant such as silicones iseliminated or greatly reduced.

The non-woven products can be used in many different applications. Usefor example in a roofing membrane is preferable as good tensile andelongation is observed. Use as a filter or a separator in battery cellsare also useful applications.

The following examples are presented to provide specific examples of thepresent invention. In each instance the thin glass plate substrate thatreceives the coating can be replaced by synthetic organic fibers. Byapplying the binder in the examples to polymeric fibers, an improvednonwoven web comprised of polymeric fibers can be achieved. It should beunderstood, however, that the invention is not limited to the specificdetails set forth in the Examples.

Formation of amine salt of inorganic acid intermediates:

To 1160 g of HMDA dissolved in 2140 g water, 980 g phosphoric acid wasadded slowly and the solution was stirred for 10 min. The intermediatewas labeled HP1/1.

Another intermediate was formed by dissolving 1160 g of HMDA in 3120 gwater. Next, 1960 g phosphoric acid was added slowly and the solutionwas stirred for 10 min. This intermediate solution was labeled HP1/2.The opaque amino-acid salt solution was utilized in the formation ofbinder.

These intermediates were utilized to make the following resins withglucose.

Example 1

To 42.8 g of solution of HP1/1 intermediate, anhydrous dextrose andwater was added. The mass of added water was chosen to be equal to thatof corresponding dextrose. The mass of dextrose (and correspondingwater) used was 72 g, 108 g, 144 g. 180 g, 216 g, 252 g, 288, 324, 360 gand 396 g. The various solutions were stirred at ambient temperature for10 min. The solutions were applied as a thin film on glass and Al panel,dried in an oven at 100° C. for 5 min and cured at 200° C. for 20 min.Each solution gave a cured brown polymer that was hard and insoluble inwater and solvents.

Example 2

To 62.4 g of solution of HP1/2 intermediate, anhydrous dextrose andwater was added. The mass of added water was chosen to be equal to thatof corresponding dextrose. The mass of dextrose (and correspondingwater) used was 72 g, 108 g, 144 g. 180 g, 216 g, 252 g, 288, 324, 360 gand 396 g. The various solutions were stirred at ambient temperature for10 min. The solutions were applied as a thin film on glass and A1 panel,dried in an oven at 100° C. for 5 min and cured at 200° C. for 20 min.Each solution gave a cured brown polymer that was hard and insoluble inwater and solvents.

Example 3

Examples 1-2 were repeated in the presence of 5% by weight ammoniumsulfate. The polymers became insoluble in water in less than 10 min.

Example 4

In a non-limiting example, a dextrose-based binder was applied tospunbond mat for evaluation of physical properties. The binder has acomposition of hexamethylenediamine/phosphoric acid/dextrose(HMDA/Phos/Dextrose) in which the molar equivalent ratios between eachcomponent are 1/2/12. The binder was diluted with tap water and appliedto a spunbond mat via a dip-and-squeeze coating application. The coatedmat was dried and cured in a standard convection oven set at 215° C.

The spunbond mat tensile and trap tear strengths were measured in boththe machine and cross-machine directions at room temperature using astandard Instron. The binder system yielded comparable tensile strengthand improved tear strength in comparison to a standard latex bindersystem.

The elongation of these spunbond mats were also measured at both roomtemperature and elevated (200° C.) temperature. The results aregraphically depicted in the FIGURE of the Drawing. In the roomtemperature test, % tensile elongation in both the machine andcross-machine directions is determined at the maximum tensile loading.The elevated temperature % tensile elongation is determined at tensileloadings of 5, 8, and 12 daN, respectively. The binder system yielded50-60% improvement in tensile elongation at elevated temperature whileproviding comparable tensile elongation at room temperature incomparison to a standard latex binder system. The overall performance ofthe binder is superior to any commercially available thermoplastic latexor formaldehyde-free thermosetting binder system and has the addedadvantage of being primarily derived from renewable raw materials.

The principles, preferred embodiments, and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rather than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

1. A process for binding polymeric fibers comprising: applying a bindercomprised of a reaction product of an aldehyde or ketone with an aminesalt of an inorganic acid to fibers of a non-woven web of polymericfibers; and curing the binder while present on the fibers.
 2. Theprocess of claim 1, wherein the salt is an amine-acid salt.
 3. Theprocess of claim 2, wherein the amine is a diamine having at least oneprimary amine group.
 4. The process of claim 3, wherein said amine isselected from the group consisting of 1,2-diethylamine,1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine,1,6-hexanediamine, α, α′-diaminoxylene, diethylenetriamine,triethylentetramine, tetraethylenepentamine, and mixtures of these. 5.The process of claim 1, wherein the acid is phosphoric acid.
 6. Theprocess of claim 1, further comprising forming an intermediatecomprising the amine salt of an inorganic acid.
 7. The process of claim6, wherein the forming comprises adding the acid to an aqueous aminesolution.
 8. The process of claim 7, wherein the acid is an oxygenatedacid selected from the group consisting of phosphoric acid,pyrophosphoric acid, phosphorus acid, sulfuric acid, sulfurous acid,nitric acid, boric acid, hypochloric acid, and chlorate acid or anon-oxygenated acid as the inorganic acid selected from the groupconsisting of hydrochloric acid, hydrogen sulfide, and phosphine.
 9. Theprocess of claim 6, further comprising adding the aldehyde or ketone tothe intermediate to produce the binder.
 10. The process of claim 9,wherein the aldehyde or ketone comprises a reducing sugar.
 11. Theprocess of claim 10, wherein the reducing sugar comprises amonosaccharide, disaccharide, or polysaccharide.
 12. The process ofclaim 9, wherein the aldehyde or ketone is added with a mass of water.13. The process of claim 12, wherein the mass of water is equal to thatof the aldehyde or ketone.
 14. The process of claim 9, furthercomprising mixing the binder at ambient temperature for a period oftime.
 15. The process of claim 1, wherein the curing comprises dryingthe binder at a first temperature for a first period of time.
 16. Theprocess of claim 15, wherein the curing further comprises curing thebinder for a second period of time at a second temperature greater thanthe first temperature.